Basic Robot
SCARA (Selective Compliance Automatic Robot Arm) robots are marketed by several manufacturers. All of these robots feature four intrinsic degrees of motion, though devices are sold to offer a further degree or two. Normally the robot has a base which may be bolted to a pedestal. Rising from this base is a column about which may rotate, in the horizontal plane, an arm. This arm has an elbow joint about which may rotate a lower arm, also strictly in the horizontal plane. At the end of this lower arm is a further joint, normally configured as a complex threaded vertical shaft, together with means to control the orientation of this vertical shaft. The threaded shaft fits into a nut which can be rotated to raise or lower the shaft, or "quill." Thus are four degrees of movement provided;
1. Rotation of the upper arm in the horizontal plane PA1 2. Rotation of the lower arm in the horizontal plane PA1 3. Rotation of the vertical quill PA1 4. Vertical movement of the quill.
The complex arrangement of the quill means that the vertical travel is limited to not much more than 12 inches. The motor to rotate the upper arm is often in the robot's base, but the other motors are usually in the arms. Drive from the motors to the axes is either direct or by means of synchronous belts or else steel bands.
Articulator
Providing extra degrees of motion to SCARA's is a difficult matter. Systems with two motors that depend from the final drive flange are on the market. These have a relatively poor strength to weight ratio and are complex and expensive.